Why we should care about our nitrogen footprint

We've all heard of carbon footprints, but we should worry about our nitrogen emissions too

Most people are familiar with a carbon footprint, but what's a nitrogen footprint?It's the total amount of nitrogen you release per year. It is linked to various areas of resource consumption, with the biggest factor being food - what you eat, how much and how that food is produced. There is also an energy component, which includes transport, housing, goods and services.

But isn't nitrogen just a naturally occurring gas? Why worry about that?For the footprint, we are concerned with reactive nitrogen - everything except the unreactive nitrogen gas (N2) that makes up about 80 per cent of our atmosphere. All other forms of nitrogen are reactive in some way and can cascade through water, the atmosphere and the land to cause a series of environmental and human health impacts. They can contribute to smog, acid rain, biodiversity loss and many other major environmental problems. It's a bit of a dilemma because we need nitrogen to survive - we consume it as protein - but when it is released to the environment it causes these problems.

You helped design a nitrogen footprint calculator. How does it work?This is a tool that is freely available online. Anyone can go to our website n-print.org to calculate their footprint. It only takes 5 to 10 minutes and you answer questions about resource consumption. The biggest of those is food, so we have scaling bars for how many times you eat different kinds of food each week, such as chicken, and so on. Then there are energy questions like electricity usage, how far you drive, how many hours you fly a year. Over 5000 people have calculated their footprint, all over the world, with big concentrations in the US, the Netherlands and Germany.

Are there any surprising results so far?I was surprised by the difference between the average US footprint and the average in the Netherlands - 41 kg per person per year in the US and about 25 kg in the Netherlands. Generally in the Netherlands there is lower food consumption, lower consumption of meat, and widespread advanced sewage treatment, which reduces the human waste footprint significantly.

What can people do to reduce their N-print?There are a number of things. One simple change is to reduce food waste. In the US we throw away over a third of our food. That's like going to the grocery store, filling up three shopping carts with food then throwing away one of those. Cut that down and you cut your footprint. Another big aspect is the amount and type of food you consume. In the US we overconsume protein, about 70 per cent more than we need.

Are there other footprints that could get the same treatment?The big one is the water footprint. That is generally done on a national basis, but there is no reason why it could not be done on a personal basis. And perhaps phosphorus as well, because of its use in fertiliser.

Profile

Allison Leach is an environmental scientist at the University of Virginia, Charlottesville, and helped develop the nitrogen footprint calculator. Find out your N-print at n-print.org

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"We need nitrogen to survive – we consume it as protein – but when it is released to the environment it causes these problems"